Such a longitudinal adjusting device comprises at least a fixed lower rail and an upper rail that is adjustable and guided in the longitudinal direction along the lower rail. Between the upper rail and the lower rail at least one linear guide for the longitudinal guidance and support of the upper rail is disposed. Usually, in such a longitudinal adjustment device two lower rails are disposed in parallel with each other in the longitudinal direction of the motor vehicle, while the motor vehicle seat is mounted to the corresponding upper rails that are adjustable and guided in the longitudinal direction along the lower rails and can be secured in their positions with respect to the lower rails.
In DE 198 12 045 A1 discloses such an adjusting device for longitudinal adjustment of a motor vehicle seat. In this longitudinal adjusting device the upper rail and the lower rail are each designed essentially as U-shaped profiles. Between the upper rail and the lower rail two bearing areas are formed, in each of which a respective linear guide is disposed. The first linear guide disposed in the first bearing area is designed for receiving forces, which act substantially in vertical direction and result from the weight of the motor vehicle seat and a load, whereas the second linear guide disposed in the second bearing area is designed for receiving forces, which act substantially in horizontal direction and also result from the weight of the motor vehicle seat and a load. The second bearing area is a substantially cylindrical hollow space in which a plurality of ball bearings are disposed acting as a linear guide. The first bearing area is formed by two substantially rectangular hollow spaces in which a plurality of rollers are disposed acting as a linear guide.
Conventional adjusting devices as outlined above will use fixed number of either balls or rollers in a respective linear guide, but do not mix them. Balls and rollers that are used as rolling elements in the prior art both have their own benefits and weaknesses. For example ball only sets are subject to brinelling of the balls or denting of the rails (the raceway of the track sliding system) and high wear, particularly when the adjusting device is adjusted to a position near a foremost or rearmost end position of the upper rails. However balls also present the lowest sliding resistance and thus lower track efforts in the seat system. On the other hand, roller only sets provide higher surface area and therefore reduced wear and brinelling but have increased rolling resistance in the application.
In the prior art, a set of rolling elements consisting either of a plurality of rollers or of a plurality of balls is usually accommodated and supported in a retainer so as to be spaced apart from each other, wherein the retainer serves as a bearing cage for reducing friction between the two rails and ensuring a comfortable, noise-free and rattle-free adjustment of the upper rail relative to the lower rail by preventing a direct contact between adjacent rolling elements. FIG. 1 shows an example of such a conventional retainer 106 for supporting a plurality of rollers 171, as disclosed in co-pending U.S. patent application Ser. No. 14/754,841 of the Applicant “Adjusting device for longitudinal adjustment of a vehicle seat and method for assembly”, filed on Jun. 30, 2016.
Referring to FIGS. 1a to 1c, retainer 106 is an oblong structure and comprises an oblong, rectangular bottom 160, in which a plurality of apertures or recesses 166, 167 for accommodating rollers 171, 172 is formed. The retainer 106 further comprises a rear side wall 161 and a front side wall 162, each extending substantially perpendicular to the bottom 160. In profile, the oblong retainer 106 is substantially L-shaped, wherein in use the oblong bottom 160 is disposed in a gap between two opposite, parallel bearing legs of the upper and lower rail, whereas the side walls 161, 162 are mated to the shape of a gap between two other opposite, parallel bearing legs of the upper and lower rail. A rectangular recess or window 165 is formed between the rear side wall 161 and front side wall 162 of retainer 106.
As shown in FIG. 1b, the recesses 166 supporting the rollers 171 are formed in the bottom 160 of retainer 106. The recesses 167 supporting the rollers 172 are formed in the rear side wall 161 and front side wall 162 (not shown) of retainer 106. The recesses 166, 167 and the rollers 171, 172 accommodated in these recesses 166, 167 are spaced apart from each other at equidistant spacing in the longitudinal direction of retainer 106. Side walls of the recesses 166, 167 extending perpendicular to the longitudinal direction of the rail (not shown) have concavely curved surfaces so that the rollers 171, 172 are snuggly accommodated in the recesses 166, 167. FIG. 1c shown the retainer of FIG. 1a in a cross-sectional view.
As shown in FIGS. 1a and 1b, only rollers 171, 172 are accommodated and supported in the recesses 166, 167 of the retainer 106. In other conventional retainers only balls are accommodated and supported in the recesses of the retainer.
In the market, there exists the need for adjusting devices for longitudinal adjustment of a vehicle seat which are as light-weight as possible, which nevertheless are stable enough to offer sufficient reliability in daily use and security in extreme situations and can be adjusted conveniently with proper adjusting forces and at reduced wear.